A "U" type neutron detection device for spent fuel burnup depth detection

Abstract

This invention discloses a U-shaped neutron detection device for detecting the burn-up depth of spent fuel, belonging to the field of non-destructive testing technology for high-level radioactive spent fuel. It includes: two opposing arm detection components; a back detection component; each arm detection component includes: a moderator material; multiple arm He-3 counters spaced apart within the moderator material; a gamma shield disposed on the outer wall of the moderator material; and a cadmium sheet disposed on the outer wall of the other side of the moderator material; the back detection component includes: a support material, with both ends of the support material fixedly connected to the ends of the two moderator materials; multiple back He-3 counters spaced apart within the support material; a base plate disposed on the outer wall of the support material; and a cable connection assembly disposed on the side of the base plate away from the spent fuel component to be measured. This invention provides dual protection for the measurement of spent fuel burn-up depth by utilizing fission neutron information and transmitted neutron information, meeting the requirements for online detection.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing technology for high-radioactivity spent fuel, specifically relating to a "U"-shaped neutron detector for detecting the burn-up depth of spent fuel. Background Technology

[0002] Burnup depth is a quantitative measure of the total energy produced per unit weight of nuclear fuel loaded into a reactor core. It is typically characterized by the thermal power released by fuel assemblies during reactor operation multiplied by operating time, and is measured in megawatt-days per ton of uranium (MWD / tU). Accurate measurement of burnup depth allows for the appropriate reduction of the critical safety margin by taking into account the consumption of fissile nuclides and the generation of fragments with neutron-absorbing properties during reactor operation, thereby achieving greater economic benefits.

[0003] Burn-up depth measurement methods are broadly categorized into destructive (DA) and non-destructive (NDA) methods. Destructive methods involve complex analytical procedures, sophisticated instruments, and can compromise the radioactive containment of spent fuel, making them unsuitable for industrial applications. Non-destructive methods, on the other hand, are widely used by spent fuel reprocessing companies and research institutions worldwide due to their simplicity, short measurement time, ease of use, and preservation of radioactive containment. Furthermore, active neutron measurement technology within the NDA category is becoming a current research hotspot due to its high detection accuracy.

[0004] Active neutron burn-down measurement techniques can be divided into delayed gamma-ray methods and neutron methods, depending on the type of particle being measured. The technique of measuring and detecting delayed gamma rays using active neutrons can only measure the burn-down depth of the fuel rods at the periphery of the component due to the self-shielding effect of the component itself against gamma rays. Furthermore, the gamma-ray background is high, resulting in limited measurement accuracy. As for active neutron measurement and neutron detection techniques, the current approach does not distinguish between fission neutrons and transmitted neutrons. Since fission neutrons decrease with increasing burn-down depth while transmitted neutrons increase, this method has relatively low measurement accuracy.

[0005] Therefore, there is an urgent need for a U-shaped neutron detection device for measuring the burnup depth of spent fuel by actively measuring and separately detecting fission neutrons and transmitted neutrons. Summary of the Invention

[0006] This invention aims to provide a U-shaped neutron detection device for measuring the burnup depth of spent fuel using active neutrons to measure and separately detect fission neutrons and transmitted neutrons. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0007] A U-shaped neutron detector for detecting spent fuel burn-up depth includes:

[0008] Two opposing arm detection components form a detection zone for the spent fuel assembly to be measured;

[0009] A rear detection component;

[0010] The arm detection assembly includes:

[0011] Moderator materials;

[0012] Multiple arm-shaped He-3 counting tubes are spaced apart within the moderating material;

[0013] A gamma shield is disposed on the outer wall of the moderator material on the side away from the spent fuel assembly to be measured, for blocking X-rays and gamma rays generated in the system;

[0014] A cadmium sheet is disposed on the outer wall of the moderator material on the side facing the spent fuel assembly to be measured, for absorbing thermal neutrons scattered from the source neutrons;

[0015] The back detection component includes:

[0016] A support material is located on one side of the detection area formed by the two arm detection components, and the two ends of the support material are fixedly connected to the ends of the two moderating materials, respectively.

[0017] Multiple back-mounted He-3 counter tubes are spaced apart within the support material;

[0018] A base plate is provided on the outer wall of the supporting material located on the side away from the spent fuel assembly to be measured.

[0019] A cable connection assembly is disposed on the side of the base plate away from the spent fuel assembly to be measured.

[0020] Furthermore, a certain distance is predetermined between the plurality of arm-type He-3 counting tubes and the outer wall of the moderator material facing the spent fuel assembly to be measured.

[0021] Furthermore, the preset distance between the arm-type He-3 counter tube and the outer wall of the moderator material facing the spent fuel assembly to be measured is 3-4 cm.

[0022] Furthermore, the moderating material is made of high-density polyethylene.

[0023] Furthermore, the moderating material has a thickness of 10-12 cm, a length of 28-32 cm, and a width of 22-23 cm.

[0024] Furthermore, multiple back He-3 counting tubes are located in the area corresponding to the detection area of ​​the support material.

[0025] Furthermore, the thickness of the cadmium sheet is set to 0.5-1.5 mm.

[0026] Furthermore, the supporting material is made of aluminum or aluminum alloy and has a thickness of 10-12 cm.

[0027] Furthermore, the effective length of the arm-shaped He-3 counter tube and the back-shaped He-3 counter tube is 203.2 mm; the pressure of the He-3 gas inside the arm-shaped He-3 counter tube and the back-shaped He-3 counter tube is 20.1 atm.

[0028] The beneficial effects of this invention are:

[0029] This invention provides a U-shaped neutron detection device for detecting the burn-up depth of spent fuel, and conducts research on measurement technology for detecting the burn-up depth of spent fuel by using active neutron-induced fission and measuring fission neutrons and transmitted neutrons.

[0030] This invention measures fission neutrons and transmitted neutrons by setting up two sets of arm-shaped detection components and one set of back-shaped detection components. Since the source neutrons utilize a moderated thermal neutron field, and fission neutrons are primarily fast neutrons, a cadmium sheet is placed on the side of the moderator material facing the component being measured to filter out thermal neutrons scattered from the source neutrons. Furthermore, the He-3 counter tube in the arm is positioned at a certain distance from the outside of the moderator material to moderate fission neutrons into thermal neutrons, increasing the detection efficiency of the He-3 counter tube. Source neutrons enter through the opening of the "U"-shaped detection device. After passing through the spent fuel assembly, some source neutrons are transmitted to the back-shaped detection component, where they are counted on the back-shaped He-3 counter tube.

[0031] Different burn-up depths of spent fuel mean different contents of fissile nuclides. This results in differences in the fission neutrons detected by the He-3 counter tube in the arm detection assembly and the transmitted neutrons detected by the He-3 counter tube in the back detection assembly, thus determining the burn-up depth of spent fuel.

[0032] This invention discloses the use of fission neutron information and transmitted neutron information to provide dual protection for the measurement of spent fuel burn-up depth, meeting the requirements of online detection. It features real-time, rapid, accurate, and non-destructive characteristics, ensuring the safe and efficient development of the nuclear energy field. Attached Figure Description

[0033] Figure 1 A front view of the U-shaped neutron detector for measuring spent fuel burn-up depth provided by the present invention;

[0034] Figure 2 This is a side view of the "U"-shaped neutron detector for measuring spent fuel burn-up depth provided by the present invention;

[0035] Figure 3 This invention relates to the response relationship between the count of the arm detection component and the spent fuel burn-out depth.

[0036] Figure 4 This invention relates to the response relationship between the count of the back detection component and the spent fuel burn-out depth.

[0037] The components include: 1. Arm detection assembly; 2. Moderation material; 3. Arm He-3 counter tube; 4. Cadmium sheet; 5. Gamma shield; 6. Back detection assembly; 7. Support material; 8. Back He-3 counter tube; 9. Base plate; 10. Cable connection assembly. Detailed Implementation

[0038] This invention provides a U-shaped neutron detector for detecting the burnup depth of spent fuel. The technical solution of this invention will be described in detail below with reference to the accompanying drawings to make it easier to understand and master.

[0039] Example 1

[0040] refer to Figure 1 - Figure 2 A U-shaped neutron detector for detecting the burn-up depth of spent fuel includes two opposing arm detector components 1 and a back detector component 6;

[0041] Among them, two opposing arm detection components 1 form a detection area for the spent fuel assembly to be measured.

[0042] In this embodiment, the arm detection component 1 includes:

[0043] Moderator material 2;

[0044] Multiple arm-shaped He-3 counting tubes 3 are spaced apart within the moderating material 2;

[0045] The γ shield 5 is disposed on the outer wall of the moderator material 2 on the side away from the spent fuel assembly to be measured, and is used to block X-rays and γ-rays generated in the system.

[0046] Cadmium sheet 4 is disposed on the outer wall of the moderator material 2 on the side facing the spent fuel assembly to be measured, and is used to absorb thermal neutrons scattered from the source neutrons.

[0047] The back detection component 6 includes:

[0048] Support material 7 is located on one side of the detection area formed by the two arm detection components 1, and the two ends of support material 7 are fixedly connected to the ends of the two slowing materials 2 respectively.

[0049] Multiple back-mounted He-3 counter tubes 8 are spaced apart within the support material 7;

[0050] Base plate 9 is set on the outer wall of the support material 7 on the side away from the spent fuel assembly to be measured;

[0051] Cable connection group 10 is located on the side of the base plate 9 away from the spent fuel assembly to be measured.

[0052] In this embodiment, a certain distance is preset between the multiple arm-type He-3 counting tubes 3 and the outer wall of the moderator material 2 facing the spent fuel assembly to be measured.

[0053] The preferred distance between the arm-type He-3 counting tube 3 and the outer wall of the moderator material 2 facing the spent fuel assembly to be measured is 3-4 cm.

[0054] In this embodiment, setting up multiple arm-type He-3 counter tubes 3 can improve detection efficiency. The arm-type He-3 counter tubes 3 are a certain distance away from the outer wall of the moderator material 2 facing the spent fuel assembly to be measured, which is used to moderate fission neutrons into thermal neutrons and increase the detection efficiency of the arm-type He-3 counter tubes 3.

[0055] In this embodiment, multiple back-side He-3 counters 8 can be used to improve detection efficiency.

[0056] In this embodiment, the moderating material 2 is made of high-density polyethylene.

[0057] The moderating material 2 has a thickness of 10-12cm, a length of 28-32cm, and a width of 22-23cm, and can play a role in fixing and supporting.

[0058] In this embodiment, multiple back He-3 counting tubes 8 are located in the area corresponding to the detection area of ​​the support material 7.

[0059] In this embodiment, the thickness of the cadmium sheet 4 is set to 0.5-1.5 mm, which can absorb most of the thermal neutrons scattered from the source neutrons.

[0060] In this embodiment, the support material 7 is made of aluminum or aluminum alloy and has a thickness of 10-12 cm.

[0061] In this embodiment, the effective length of the arm-shaped He-3 counter tube 3 and the back-shaped He-3 counter tube 8 is 203.2 mm; the pressure of the He-3 gas inside the arm-shaped He-3 counter tube 3 and the back-shaped He-3 counter tube 8 is 20.1 atm.

[0062] The "U"-shaped neutron detector for spent fuel burn-out depth detection provided in this embodiment has an environmental radiation dose equivalent rate of less than 2.5 uSv / h at 30 cm from the outer surface of the γ shield 5, which meets national safety standards.

[0063] The "U"-shaped neutron detector for spent fuel burn-up depth detection provided by this invention operates on the following principle:

[0064] When the component under test is irradiated by source neutrons, the fissile nuclides within it will undergo fission, producing fission neutrons. At the same time, they absorb source neutrons, resulting in a reduction of source transmitted neutrons. Among them, fission neutrons are mainly fast neutrons, while source neutrons are thermal neutron fields that have been slowed down.

[0065] Cadmium has a large absorption cross-section for thermal neutrons, so the cadmium sheet 4 filters out the scattered source neutrons in the fission neutrons. The moderator material 2 can slow down the fission neutrons into thermal neutrons and hyperthermal neutrons. The arm-shaped He-3 counter tube 3 has a large detection efficiency for the slowed thermal neutrons and hyperthermal neutrons, forming a fission neutron count.

[0066] For the back detection component 6, both source neutrons and fission neutrons are incident on the back He-3 counter tube 8. Since these neutrons are not slowed down, the back He-3 counter tube 8 will only respond to the source transmitted neutrons, which are originally thermal neutrons, thus forming a transmitted neutron count.

[0067] More specifically, source neutrons enter through the opening of the "U"-shaped detection device. After passing through the spent fuel assembly, some source neutrons are transmitted to the back detection assembly, where they are counted on the back He-3 counter tube. Different burn-up depths in the spent fuel indicate different contents of fissile nuclides. Consequently, the fissile neutrons detected by the arm He-3 counter tube 3 in the arm detection assembly and the transmitted neutrons detected by the back He-3 counter tube 8 in the back detection assembly will differ, thus determining the burn-up depth of the spent fuel.

[0068] Based on the fission neutron intensity measured by the He-3 counter tube 3 in the arm, the transmitted neutron intensity measured by the He-3 counter tube 8 in the back, and... Figure 3 and Figure 4 The established response relationship can provide dual assurance for the measurement of burn-up depth of spent fuel assemblies.

[0069] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0070] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A U-shaped neutron detector for detecting spent fuel burn-up depth, characterized in that, include: Two opposing arm detection components form a detection zone for the spent fuel assembly to be measured; A rear detection component; The arm detection assembly includes: Moderator materials; Multiple arm-shaped He-3 counting tubes are spaced apart within the moderating material; A gamma shield is disposed on the outer wall of the moderator material on the side away from the spent fuel assembly to be measured, for blocking X-rays and gamma rays generated in the system; A cadmium sheet is disposed on the outer wall of the moderator material on the side facing the spent fuel assembly to be measured, for absorbing thermal neutrons scattered from the source neutrons; The back detection component includes: A support material is located on one side of the detection area formed by the two arm detection components, and the two ends of the support material are fixedly connected to the ends of the two moderating materials, respectively. Multiple back-mounted He-3 counter tubes are spaced apart within the support material; A base plate is provided on the outer wall of the supporting material located on the side away from the spent fuel assembly to be measured. A cable connection assembly is disposed on the side of the base plate away from the spent fuel assembly to be measured; In this process, when the component under test is irradiated by source neutrons, the fissile nuclides within it undergo fission, producing fission neutrons. Simultaneously, they absorb source neutrons, resulting in a reduction in the number of source-transmitted neutrons. Among these fission neutrons, fast neutrons are predominant, while source neutrons are moderated thermal neutron fields. Cadmium has a large absorption cross-section for thermal neutrons, so the cadmium sheet filters out scattered source neutrons from the fission neutrons. The moderator material can moderate the fission neutrons into thermal and hyperthermal neutrons. The He-3 counter tube in the arm has a high detection efficiency for the moderated thermal and hyperthermal neutrons, thus forming a fission neutron count. For the back detection component, both source neutrons and fission neutrons are incident on the back He-3 counter. Since these neutrons are not slowed down, the back He-3 counter will only respond to the source transmitted neutrons, which are originally thermal neutrons, thus forming a transmitted neutron count. Source neutrons enter through the opening of the "U"-shaped detector. After passing through the spent fuel assembly, some source neutrons are transmitted to the back detector assembly and counted on the back He-3 counter tube. Different burn-up depths of spent fuel mean different contents of fissile nuclides. Therefore, the fissile neutrons detected by the arm He-3 counter tube in the arm detector assembly and the transmitted neutrons detected by the back He-3 counter tube in the back detector assembly will be different, thus obtaining the burn-up depth of spent fuel. Based on the fission neutron intensity measured by the He-3 counter tube in the arm, the transmitted neutron intensity measured by the He-3 counter tube in the back, and the established response relationship, dual assurance can be provided for the measurement of the burnup depth of spent fuel assemblies.

2. The "U"-shaped neutron detector for spent fuel burn-up depth detection according to claim 1, characterized in that, A certain distance is predetermined between the multiple arm-type He-3 counting tubes and the outer wall of the moderator material facing the spent fuel assembly to be measured.

3. The "U"-shaped neutron detector for spent fuel burn-up depth detection according to claim 2, characterized in that, The preset distance between the arm-mounted He-3 counter tube and the outer wall of the moderator material facing the spent fuel assembly to be measured is 3-4 cm.

4. The "U"-shaped neutron detector for detecting spent fuel burn-up depth according to claim 1, characterized in that, The moderating material is made of high-density polyethylene.

5. The "U"-shaped neutron detector for spent fuel burn-up depth detection according to claim 4, characterized in that, The moderating material has a thickness of 10-12 cm, a length of 28-32 cm, and a width of 22-23 cm.

6. The "U"-shaped neutron detector for spent fuel burn-up depth detection according to claim 1, characterized in that, Multiple back-mounted He-3 counter tubes are located in the area corresponding to the detection area of ​​the support material.

7. The "U"-shaped neutron detector for spent fuel burn-up depth detection according to claim 1, characterized in that, The thickness of the cadmium sheet is set to 0.5-1.5 mm.

8. The "U"-shaped neutron detector for spent fuel burn-up depth detection according to claim 1, characterized in that, The supporting material is made of aluminum or aluminum alloy and has a thickness of 10-12cm.

9. The "U"-shaped neutron detector for spent fuel burn-up depth detection according to claim 1, characterized in that, The effective length of the arm-shaped He-3 counter tube and the back-shaped He-3 counter tube is 203.2 mm; the pressure of the He-3 gas inside the arm-shaped He-3 counter tube and the back-shaped He-3 counter tube is 20.1 atm.

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